Several properties of phosphazene polymers (R2PN)x would seem to make them ideal for the immunogenic delivery of a wide variety of antigens. First, they readily form covalent linkages with those reactive groups common to polypeptides, carbohydrates, and many small organic molecules. Second, at physiologic pH, the controlled hydrolysis of the P-N bonds results in fragmentation of the polymer and the concomitant release of smaller (P=N)x units. Third, the degradation products of the polymer are on-toxic. Phosphazene polymers partially substituted with haptens and protein will be synthesized and injected into mice. Evidence of a cellular and/or humoral response will then be investigated. Establishing the effectiveness of this antigen delivery system is an important step in determining its suitability for a wide variety of immunologic applications. As an adjuvant, phosphazenes would allow the steady release of antigens covalently attached to the polymer. Experiments testing the usefulness of polyphosphazenes as adjuvants would be of special interest to the IAID program of the NIAID. Phosphazenes could also be used for the antigenic modification of the tumor cell surface. Application of a partially haptenated phosphazene to the tumor cell surface could covalently link haptens to tumor-specific antigens via the phosphazene polymer. This could create new, highly immunogenic determinants.